1. Field of the Invention
The present invention relates generally to an optical weft sensor for a loom and more specifically to the installation position or installation method of an optical weft sensor for use with a fluid-jet loom.
2. Description of a Prior Art
As is well known, an optical weft sensor is provided for a fluid-jet loom (air-jet loom or water-jet loom) in order to optically detect that a weft thread is securely inserted into fluid-guide plates having a fluid-guide opening and a weft-removing slot, respectively, and arranged in the direction of weft insertion. The optical weft sensor comprises a light-emitting section and a light-receiving section for detecting the presence or absence of weft depending upon the change in magnitude of the received light, which is caused when a weft removed through the weft-removing slot of the fluid-guide plate passes across an optical axis formed between the light-emitting section and the light-received section during the beat-up stage.
In the prior-art optical weft sensor, however, there exist some problems or shortcomings as follows:
1. Since the light-emitting element (e.g. diode) and the light-receiving element (e.g. phototransistor) are disposed on the fluid-guide plates or fixed to a certain position on the reed frame, shock or vibration caused by the oscillating reed is inevitably applied to the light-emitting element and the light-receiving element, thus resulting in a problem in that these electronic elements may easily be damaged.
2. since the presence or absence of the weft is detected depending upon the instantaneous change in magnitude of the received light caused when a weft is removed through the weft-removing slot, the weft detection time period is short, thus resulting in a problem in that it is difficult to discriminate an optical signal due to weft from that due to fluff; that is, there exist erroneous detections;
3. since the optical weft sensor is mounted near the weft-removing slot of one of the fluid-guide plates, the optical weft sensor is sometimes brought into contact with the weft removed through the weft-removing slot at the beat-up stage and therefore pushes the removed weft toward the cloth fell, thus resulting in a problem in that the weft vibrated by the sensor applies undesirable vibrations to the selvedge (leno) yarns and catch-cord yarns; that is, there exist wale streak and misscatching of weft;
4. since the optical weft sensor is directly mounted on or in one of the fluid-guide plates or between two of the fluid-guide plates, thus resulting in a problem in that when the width of woven cloth is required to change, the setup work is troublesome and takes much preparatory time.
A more detailed description of the prior-art optical weft sensor for a fluid-jet loom will be made with reference to the attached drawings under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.